I highly recommend the whole rhythm heaven (rizumu tengoku if your trying to find the japanese exclusice(s)) it's absolutly fantastic and packed to the brim with content and fun.
Winner of Emerald's Spring osu! 25k to 45k Aus/NZ Tournament! (Osu!std) Quarter finalist of Osu Friendly Tournamnet 20k-60k! (Osu!std) Participant in the Ausu! 4k Mania Tournament
I'm pretty attached to Taiko because it's the first rhythm game I've been introduced to, but honestly at this point it's probably Pop'n Music.
Though I can't really decide,the games I've played before (Aside from the two I've mentioned there's Ouendan+EBA,Jubeat,Reflec Beat, Beatmania IIDX,Sound Voltex,Groove Coaster Zero,Cytus,Deemo and Dynamix) are all pretty good in their own ways.
Cytus is the only rhythm game I actually play decently. It's pretty amazing because of the fact there is a theme and a storyline (along with recurring sub-storylines). Deemo (based from what I've watched) is pretty enjoyable too although I haven't played it that much. How am I able to fit two games which takes up to 1 gig each in a phone that has only 16 gig storage space? Another rhythm game I tried to play was Malody. It has most of the modes that you can imagine. That's if, you can imagine it.